a(n) = n*(9*n - 1)/2.

Terms

a(0) =0a(1) =4a(2) =17a(3) =39a(4) =70a(5) =110a(6) =159a(7) =217a(8) =284a(9) =360a(10) =445a(11) =539a(12) =642a(13) =754a(14) =875a(15) =1005a(16) =1144a(17) =1292a(18) =1449a(19) =1615a(20) =1790a(21) =1974a(22) =2167a(23) =2369a(24) =2580a(25) =2800a(26) =3029a(27) =3267a(28) =3514a(29) =3770